Charles Fort's Book of the Damned (1919) was an important inspiration for H. P. Lovecraft, and Fort followed the Theosophists in imagining ancient astronauts coming to earth. In the book, he presents a fascinating example of an early ancient astronaut claim that would find its way, almost wholesale, into Chariots of the Gods and dozens of other ancient astronaut books. In this passage Fort speculates on alien ("extra-mundane") visitors to ancient earth and the masks they would need to wear to visit our planet:

from The Book of the Damned (1919)

_If I say I conceive of another world that is now in secret communication with certain esoteric inhabitants of this earth, I say I conceive of still other worlds that are trying to establish communication with all the inhabitants of this earth. I fit my notions to the data I find. That is supposed to be the right and logical and scientific thing to do; but it is no way to approximate to form, system, organization. Then I think I conceive of other worlds and vast structures that pass us by, within a few miles, without the slightest desire to communicate, quite as tramp vessels pass many islands without particularizing one from another. Then I think I have data of a vast construction that has often come to this earth, dipped into an ocean, submerged there a while, then going away—Why? I'm not absolutely sure. How would an Eskimo explain a vessel, sending ashore for coal, which is plentiful upon some Arctic beaches, though of unknown use to the natives, then sailing away, with no interest in the natives?

A great difficulty in trying to understand vast constructions that show no interest in us:

The notion that we must be interesting.

I accept that, though we're usually avoided, probably for moral reasons, sometimes this earth has been visited by explorers. I think that the notion that there have been extra-mundane visitors to China, within what we call the historic period, will be only ordinarily absurd, when we come to that datum.

I accept that some of the other worlds are of conditions very similar to our own. I think of others that are very different—so that visitors from them could not live here—without artificial adaptations.

How some of them could breathe our attenuated air, if they came from a gelatinous atmosphere--

Masks.

The masks that have been found in ancient deposits.

Most of them are of stone, and are said to have been ceremonial regalia of savages--

But the mask that was found in Sullivan County, Missouri, in 1879 (American Antiquarian, 3-336).

It is made of iron and silver.

If you didn't know better, you'd swear Erich von Daniken wrote this. Von Daniken makes the same claim that ancient people could not understand alien vessels, that the aliens explored the earth, and that they wore helmets of masks to breath our air, and that the ancient people imitated these astronaut suits in their art.

There is nothing original in the ancient astronaut theory as presented by its modern proponent, only reworkings of outdated old theories that few believed the first time around.